What causes roof stains

[Rusty Keith]

I know you veterans will know this. I live in Florida and have wondered what causes the dark stains common on roofs. They are like streaks but are not visible under vents. It is like the vents shed what ever is causing the stains from getting on the shingles located down the slope from the vents.
Thanks

[Michael R. Boyett]

Here's my standard verbiage for this issue:

One or more sections of the roof covering appear stained. An algae known as Gloeocapsa Magma is the most likely culprit and this algae affects nearly 80 percent of the homes across the United States. Gloeocapsa Magma is a species of algae that causes black streaking and discoloration on asphalt/fiberglass shingles. The black staining you see on many roofs is caused by the life cycle of algae and fungus spores that land on houses via wind or wildlife. While this algae can grow just about anywhere, it prefers humid environments. A preferred food source of this algae is limestone which is used as "filler material" by most shingle manufactures. Higher quality shingles are manufactured with preventative measures such as copper or zinc containing granules. Several methods exist to prevent and clean infected areas. Installing zinc or copper strips near the roof ridge can prevent further algae growth. Application of bleach (non-chlorine) can aid in removing the stains, as well as many available commercial cleaning products. Some products may harm vegetation beneath roof eaves or near downspout extensions. While many remedies can be performed by the home owner, we recommend the use of qualified professionals due to the extreme danger and risk of injury or death associated to roof repairs and cleaning.

[rcooke]

Originally Posted by rkeith

I know you veterans will know this. I live in Florida and have wondered what causes the dark stains common on roofs. They are like streaks but are not visible under vents. It is like the vents shed what ever is causing the stains from getting on the shingles located down the slope from the vents.
Thanks

If the vents are made from Galvanised this will stop mould from growing . In sever areas here they put down a zink strip at the edghe of the first row of shingles and this stops it .
Lots of info here .http://www.ronhungarter.com/
Roy Cooke

[Doug Edwards, CMI]

Gloeocapsa magma (a very hardy algae). The zinc in the metal "through the roof" vents, etc kills the algae. The dark stains and streaks you are seeing is mostly the dead algae cells. Harmless for the most part except it darkens the roof, causing more absorbsion of heat, etc. etc. Durashield http://www.durashield.com/ is one product used to get rid of it and preventing its return for a short time.

[David P. Valley]

http://www.cleanertoday.com/

[Rusty Keith]

Thanks folks,
That solves the mistry.
Rusty

[Brian A. MacNeish]

Originally Posted by rcooke

Lots of info here .http://www.ronhungarter.com/
Roy Cooke

Roy:

Went to the Hungarter site and was dismayed he has not been involved in upgrading his Building Science. Not one mention about airsealing the attic to stop air and water vapour leakage from the house.

Adding vents to take care of attic moisture, improve shingle life, reduce ice dams, reduce air conditioning bills are all old hat. Research from the last 20-30 years has dispelled some widely held "facts".

For example: The 1 to 300 rule for attic vent requirements is a code regulation here but has been disproven by some historical and recent research. The rule came out of research on vapour barriers (not attic ventilation) at Penn State University in 1947-8. It was never tested in a scientific manner until recently and has been found to be lacking. As stated in a 1993 article titled "The Mysterious Origins of the 1:300 Rule" (in Energy Design Update- a pricey newsletter from Vermont; US $385/year or $1.50/page):

"After an extensive search for the roots of the 1:300 rule, (building science researcher Bill) Rose found it was hastily derived from a single lab experiment on a flat roof. The vent-to-roof ratio, 1:300, appears to be merely an incidental detail peculiar to the test setup. For want of a better number, the 1:300 ratio was subsequently adopted as good building practice and was eventually added to building codes."

A good piece from the CMHC About Your House series is "Attic Venting, Attic Moisture and Ice Dams"
See http://www.cmhc.ca/en/co/maho/gemare/gemare_001.cfm

I've been working in energy efficiency and conservation since 1977 and feel that the boat is being missed regularly on the attic issues since most of the trades are not required to re-train or get CEU's to maintian their licenses or contractor status. Many guys like Hungarter, Shel Busey in BC and Ren Molnar and Mike Holmes get on radio/TV shows not because of their in depth building knowledge but because of having a show idea first or for their personalities.


Regards,
Brian MacNeish

[rcooke]

Originally Posted by Brian A. MacNeish

Roy:

Went to the Hungarter site and was dismayed he has not been involved in upgrading his Building Science. Not one mention about airsealing the attic to stop air and water vapour leakage from the house.

Adding vents to take care of attic moisture, improve shingle life, reduce ice dams, reduce air conditioning bills are all old hat. Research from the last 20-30 years has dispelled some widely held "facts".

For example: The 1 to 300 rule for attic vent requirements is a code regulation here but has been disproven by some historical and recent research. The rule came out of research on vapour barriers (not attic ventilation) at Penn State University in 1947-8. It was never tested in a scientific manner until recently and has been found to be lacking. As stated in a 1993 article titled "The Mysterious Origins of the 1:300 Rule" (in Energy Design Update- a pricey newsletter from Vermont; US $385/year or $1.50/page):

"After an extensive search for the roots of the 1:300 rule, (building science researcher Bill) Rose found it was hastily derived from a single lab experiment on a flat roof. The vent-to-roof ratio, 1:300, appears to be merely an incidental detail peculiar to the test setup. For want of a better number, the 1:300 ratio was subsequently adopted as good building practice and was eventually added to building codes."

A good piece from the CMHC About Your House series is "Attic Venting, Attic Moisture and Ice Dams"
See http://www.cmhc.ca/en/co/maho/gemare/gemare_001.cfm

I've been working in energy efficiency and conservation since 1977 and feel that the boat is being missed regularly on the attic issues since most of the trades are not required to re-train or get CEU's to maintian their licenses or contractor status. Many guys like Hungarter, Shel Busey in BC and Ren Molnar and Mike Holmes get on radio/TV shows not because of their in depth building knowledge but because of having a show idea first or for their personalities.


Regards,
Brian MacNeish

Thanks Brian I have not been to his site in a while .
The reason I used him is because he was the first one I know of who talked about zink to stop moss .
Got to love NACHI so many great ideas come from all .
Thanks again . Roy Cooke